Alzheimer's disease (AD) is a complex, heterogeneous, progressive neurodegenerative disease and is the most common form of dementia with prevalence estimates ranging from 14% at age 65 or older to more than 40% at age 85 or older (Changing the Trajectory of Alzheimers Disease: A National Imperative. Alzheimer's Association 2010; 2012 Alzheimer's Disease Facts and Figures. Alzheimer's Association 2012). In 2010, the Alzheimer's Association estimated that 35.6 million people worldwide would be living with a diagnosis of dementia and that the number of diagnosed dementia patients would nearly double every 20 years, leading to 65.7 million patients by 2030. This number indicates that dementia is rapidly becoming a major threat to healthcare. According to the Alzheimer's Association, delaying the onset of dementia by only a 5-year interval would decrease U.S. healthcare cost for dementia by almost 50% (Changing the Trajectory of Alzheimers Disease: A National Imperative. Alzheimer's Association 2010; 2012 Alzheimer's Disease Facts and Figures. Alzheimer's Association 2012). In response to this increasing healthcare threat, ten (10) Phase III clinical trials have been completed in AD over the past ten (10) years. All ten (10) clinical trials resulted in treatment failures. To date, no good therapeutic options are available, nor is there a cure for AD.
Over the past decade, understanding of the pathogenesis of AD has rapidly increased. There include characteristic pathologic changes (e.g., Aβ plaques, neurofibrillary tangles, neuronal cell loss, etc.) and prominent activation of a microglial/astrocytic immune/inflammatory process in AD patient brains, as well as in AD animal models. These abnormalities in pathology and disordered immune activation have led to the hypothesis that certain inflammatory cytokine mediators may be driving the Alzheimer's disease process (Wyss-Coray T. et al., J. Inflammation in Alzheimer's Disease-A Brief Review of the Basic Science and Clinical Literature, Cold Spring Harbor Perspect. Med. 2012; 2(1):a006346; Glass, C. K. et al., Mechanisms Underlying Inflammation in Neurodegeneration, Cell, 2010, 140: 918-934; Zilka, N. et al., Who Fans the Flames of Alzheimer's Disease Brains? Misfolded Tau on the Crossroad of Neurodegenerative and Inflammatory Pathways, J. Neuroinflammation, 2012, 9: 47).
New information has implicated a flawed innate immune response in the development of late onset Alzheimer's disease (Wyss-Coray T. et al., J. Inflammation in Alzheimer's Disease-A Brief Review of the Basic Science and Clinical Literature, Cold Spring Harbor Perspect. Med. 2012; 2(1):a006346; Glass, C. K. et al., Mechanisms Underlying Inflammation in Neurodegeneration, Cell, 2010, 140: 918-934; Zilka, N. et al., Who Fans the Flames of Alzheimer's Disease Brains? Misfolded Tau on the Crossroad of Neurodegenerative and Inflammatory Pathways, J. Neuroinflammation, 2012, 9: 47). For example, Stefansson et al. described a new missense mutation (R47H) present in a gene coding for the triggering receptor expressed on myeloid-derived cells 2 (called TREM-2) (Jonsson, T. et al., N Engl. J. Med., 2013, 368: 107-116, DOI: 10.1056/NEJMoa1211103; Guerreiro, R. et al, N Engl. J. Med., 2012, DOI: 10.1056/NEJMoa1211851; Piccio, L. et al., Eur. J. Immuno., 2007, 37: 1290-1301; Neumann, H. et al., Neruoimmunol., 2007, 184: 92-99). TREM-2 is an innate immune receptor highly expressed on immature dendritic cells, microglia, and osteoclasts. It is involved in phagocytosis of neural debris in the brain and it concomitantly down-regulates pro-inflammatory cytokine production. Homozygous loss-of-function TREM-2 mutations have been previously linked to an early onset of dementia coupled with bone abnormalities. Stefansson et al. reported that the heterozygous TREM-2 missense genetic variant provoked a loss-of-function (i.e., impaired innate immune regulation). Such loss-of-function resulted in a failure to block pro-inflammatory cytokine production, which in turn, fueled rampant inflammation in the AD brain. In addition to a loss-of-function, Stefansson et al. reported that the TREM-2 missense genetic variant was associated with a significant increase in the risk of late onset Alzheimer's disease (See also, Jonsson, T. et al., N Engl. J. Med., 2013, 368: 107-116, DOI: 10.1056/NEJMoa1211103; Guerreiro, R. et al., N Engl. J. Med., 2013, 368: 117-127, DOI: 10.1056/NEJMoa1211851).
In addition to the work of Stefansson et al., another investigator, Relkin et al., who has treated small numbers of mild to moderate AD patients with pooled intravenous immunoglobulin (IVIG) as a possible immunotherapy (Relkin, N. et al., AAIC 2012: abstract P3-381), and reported that AD patients treated with IVIG showed a decreased rate of ventricular enlargement in association with a reduction in whole brain atrophy and less cognitive impairment compared to a group of AD patients treated with placebo (i.e., control group). Despite its potential as an AD therapy, insufficient supply of pooled IVIG on a worldwide basis making its use problematic.
Thus, the need exists to develop alternative sources of immune modifying agents to delay onset and/or progression of the neurodegenerative process in patients suffering from AD and other neurodegenerative diseases (Hughes, R. A. et al., Clin. and Exp. Immunol., 2009, 158 (Suppl. 1); 34-42).
Erythropoietin (EPO), a 165 amino acid glycoprotein hormone initially identified as a hematopoietic growth factor, has been used extensively for the treatment of anemia in humans. Recently, EPO has received considerable attention due to its potential neuroprotective capabilities following brain and central nervous system (CNS) injury (Yuan, R. et al., PLoS 2008 3:e1924; Brines, M. L. et al., Proc. Natl. Acad. Sci. USA, 97: 10526-31 (2000); Siren, A. L. and Ehrenreich, H., Eur. Arch. Psychiatry Clin. Neurosci., 251: 179-184 (2001); Buemi, M. et al., J. Neuropathol. Exp. Neurol., 62: 228-236 (2003); Li, W. et al., Ann. Neurol., 56: 767-777 (2004); Sakanaka, M. et al., Proc. Natl. Acad. Sci. USA, 95: 4635-4640 (1998)). Exogenously administered EPO has been shown to significantly reduce neurologic impairment in several diverse forms of neurologic injury (e.g., acute brain trauma, epilepsy, autoimmune model of demyelinating disease, etc.) (Brines, M. L. et al., Proc. Natl. Acad. Sci. USA, 97: 10526-31 (2000); Li, W. et al., Ann. Neurol., 56: 767-777 (2004); Tsai, P. T. et al., J. Neurosci., 26: 1269-1274 (2006); Buemi, M. et al., Clin. Sci. (Loud), 103: 275-282 (2002)). However, long-term EPO therapy remains significantly limited in non-anemic patients with neurological injury, because administration of EPO in these patients may overly stimulate erythropoiesis leading to serious side-effects such as heart attack and stroke. In order to overcome these serious side-effects, EPO therapy would have to be limited to short-term use, or alternatively, to the use of other EPO molecular preparations (e.g., fragments, mutants, etc.) devoid of hematopoietic effects. Indeed, molecular preparations such as an asialo-form of EPO, carbamylated EPO (CEPO) and certain EPO mutants have been shown to be neuroprotective in animals following experimental traumatic spinal cord injury or acute stroke without provoking an increase in red blood cell production (Erbayrakar, S. et al., Proc. Natl. Acad. Sci. USA, 100: 6741-6746 (2003); Leist, M. et al., Science, 305: 239-242 (2004); Mun, K. C. and Golpher, T. A., Blood Purif., 18: 13-17 (2000); Brines, M. et al., Proc. Natl. Acad. Sci. USA, 101: 14907-14912 (2004)). In addition, a seventeen (17) amino acid EPO-derived linear peptide was reported to have neuroprotective effects in vitro (Campana, W. M. et. al., Int'l J. Mol. Med., 1: 235-241 (1998)).
The present inventors have synthesized a library of short, stabilized EPO-derived peptides, which induce substantial neuroprotective immunomodulatory effects in acute murine models of human multiple sclerosis and acute traumatic brain injury (US 2009/0029906). These synthetic, short, stabilized peptides were derived from a distinct domain embedded within the early sequence of the EPO molecule. Whereas the full-length EPO molecule is manufactured by an expensive cell culture process based on CHO cells, the synthetic, short, stabilized EPO-derived peptides provide the advantage of low manufacturing costs, low immunogenicity, and high stability (US 2009/0029906; US 2011/0190217). Notably, these EPO-derived peptides are devoid of hematopoietic effects. A lead compound, JM4 (GCAEHCSLNENITVPDTKV; SEQ ID NO: 1), a stabilized, cyclic peptide derived from the first loop of erythropoietin, has been evaluated in vitro and in vivo. To date, JM4 shows considerable promise as a potent immune/inflammatory modulator useful for treating animal experimental autoimmune encephalomyelitis (EAE) and for treating murine acute brain injury. JM4 shows good efficacy in animals and the preliminary side effect profile is highly favorable compared to whole molecule erythropoietin.
JM4 exhibits robust immunomodulation in several pre-clinical animal models, including EAE, brain trauma and collagen II induced autoimmune arthritis, but does not depress overall amounts of B- or T-cells, Instead, JM4 favorably modulates the ratio of T-suppressor (Treg) to T helper 17 (Th-17) effector cells. JM4 also strongly down-regulates antigen specific T-cell proliferation through its effect on dendritic cells or microglia (innate immunity). JM4 also blocks pro-inflammatory cytokine production. The medicinal attractiveness of these EPO-derived peptides is underscored by the observation that JM4 treated mice appear normal and lack any effects on hematopoiesis and blood chemistries.
In animal models of dementia, we have found EPO-derived peptides are capable of delaying the onset of disease and delaying progression of dementia and prolonging overall survival of subjects. Neurofibrillary tangles (NFTs) are aggregates of the microtubule-associated protein “tau”, which have become hyperphosphorylated and accumulate inside the cells themselves. Tau is relatively abundant in neurons but is present in all nucleated cells and functions physiologically to bind microtubules and stabilize microtubule assembly for polymerization. In one of our models of neurodegenerative disease, the EPO-derived peptide prevented ventricular enlargement, blocked over-expression of tau protein and over-expression of major histocompatibility complex class II (MHC II) in microglial cells.